1. Field of the Invention
The invention relates to a collision detection apparatus that is, for example, mounted in a vehicle, and that determines whether an object has collided with a side surface of the vehicle from outside, and to a collision determination method therefore. Besides, the invention also relates to an activation control apparatus for an occupant protection apparatus which is, for example, mounted in a vehicle, and which determines whether an object has collided with a side surface of the vehicle from outside, and which controls activation of the occupant activation device.
2. Description of the Related Art
In order to appropriately protect an occupant of a vehicle by an occupant protection apparatus, such as an airbag or the like, which protects an occupant of a vehicle at the time of a collision of the vehicle, it is necessary to accurately determine whether the vehicle has collided. Therefore, various devices, methods, etc. for determining whether a vehicle has collided are described (e.g., see Japanese Patent Application Publication No. 2009-090717 (JP-A-2009-090717). A collision detection apparatus described in Japanese Patent Application Publication No. 2009-090717 (JP-A-2009-090717) determines whether a collision of an object with a door portion of the vehicle from outside has occurred on the basis of the direction and magnitude of the acceleration that occurs on the door portion, and the sign of the value obtained by integrating the acceleration that occurs on the door portion over a predetermined time.
According to the collision detection apparatus described in Japanese Patent Application Publication No. 2009-090717 (JP-A-2009-090717), it is possible to prevent false determination that an object has collided with a door portion of the vehicle from outside when the door portion is merely closed hard.
However, in the collision detection apparatus described in Japanese Patent Application Publication No. 2009-090717 (JP-A-2009-090717), when a vehicle is traveling on a rough road, or when a door portion is closed hard, or the like, there is possibility of occurrence of a delay in the timing of determining that an object has collided with the door portion of the vehicle from outside, due to effect of an integral of the acceleration that occurs on the door portion.
That is, the technology proposed in the collision detection apparatus described in Japanese Patent Application Publication No. 2009-090717 (JP-A-2009-090717), when an object collides with the door portion from outside, positive acceleration occurs, and the integral of acceleration (=the velocity) is a positive value, provided that the positive direction is defined as the direction from the outside of the door portion to the inside thereof. Therefore, if the acceleration that occurs on the door portion is greater than or equal to a pre-set positive threshold value, and the integral of acceleration (=the velocity) is positive, it is determined that an object has collided with the door portion from outside (see FIG. 14).
However, for example, in the case where an object collides with the door portion from outside while a negative value is found as an integral of acceleration (=a velocity), for example, during a travel of the vehicle on a rough road, it is not until the integral of acceleration (=the velocity) becomes positive that it is determined that an object has collided with the door portion from outside. Thus, there occurs a delay in the timing of determining that an object has collided with the door portion from outside (see FIG. 15).